The symmetrical chirp effects on the momentum spectrum and reduced particle number can also be discussed in terms of the turning point structure of potential in semiclassical regime by employing complex Wentzel-Kramers-Brillouin (WKB) scattering approach. The scattering potential is determined by solving the equation \(\omega _{\bf p}(t)= \sqrt{m^{2}+p_{\perp }^{2}+(p_{x}-eA(t))^{2}}=0\)  for the turning points which appear as complex conjugate pairs when the potential is real [1]}. When a single complex turning point dominates, the WKB results for the particle creation rate is given as [2]}, [3]}
\(N_{\rm }\approx e^{-2K} , \qquad K=\left| \int _{t_1}^{t_2} \omega (t)\, dt\, \right|,\) 
